Structure/Function Characterization of Post-Trabeculectomy Cataract in Rabbits

Abstract

Abstract: : Purpose: Trabeculectomy very frequently leads to cataract. We have used an animal model (rabbit) to characterize lens structure/function changes in post-trabeculectomy cataract. Methods: Trabeculectomy was performed on 3 mth old Dutch-belted rabbits either with BSS PLUS (n=7) or with mitomycin C treatment (0.5mg/mL; n=14). Age-matched un-operated rabbits were used as controls. Post-surgical intra-ocular pressure (IOP), blood aqueous barrier (BAB) leakage and lens transparency were monitored periodically until sacrifice 3 mths after surgery. Lens function (avg. back vertex distance, BVD and sharpness of focus [spherical aberration or variability in BVD]) at the time of sacrifice was quantified by low power helium neon laser scan analysis. The above data was then correlated with lens structure shown in 3D-CAD reconstructions derived from SEM micrographs. Results: Slit-lamp examination revealed no cataracts in either any control lens or any lens from operated eyes with BSS PLUS treatment. In contrast, cataracts (cortical and posterior subcapsular) were noted in >50% of lenses from operated eyes with mitomycin C adjunct therapy. Structural analysis revealed that the lens from "each" operated eye had an abnormal sub-branch that extended from the nasal, posterior suture branch directly toward the surgical site. This sutural alteration appeared to cause a concomitant "bending" of the anterior suture. The length of the abnormal, sub-branch, its complexity (additional tertiary branches extending from the sub-branch), and extent of anterior suture bending, were correlated with functional compromise (control lenses: avg. BVD = 17.19±0.14mm and variability in BVD = 0.394±0.034 vs. lenses from operated eyes with BSS PLUS: avg. BVD = 17.05±0.09 and variability in BVD = 0.35±0.04) and subsequent cataract formation (lenses from operated eyes with mitomycin C: avg. BVD = 16.87±0.30 and variability in BVD = 0.62±0.14). Cataract formation was also strongly correlated with greater BAB leakage (Fluourescein leakage [Kp = min^-1 x 10^-3]: control eyes = 1.28±0.34 vs. operated eyes with BSS PLUS =1.13±0.95 vs. operated eyes with mitomycin C = 3.8±5.1) but not with IOP. Conclusions: Correlative structure/function analysis of rabbit lenses following trabeculectomy show that this ocular surgery results in sutural defects that are further exacerbated by adjunct therapy manifest as degradation in optical quality and cataractogenesis.

Keywords: cataract • animal model • microscopy: electron microscopy